While the invention has other applicability it is especially suited to the measurement of temperature in medical and veterinary applications. Measurement is accomplished with a probe which is connected to signal processing and indicating unit to form the measurement system. For practical reasons it is the practice that the probe be made disposable and not reused. The measurement is made electrically. The probe provides an electrically-measurable signal which varies as a function of temperature. Two forms of sensor are in common use: one is a thermistor, the resistance of which varies with temperature; the other is a thermocouple in which potentials are developed which are a function of temperature.
Thermocouple probes are less costly than are thermistor probes. Because the probes are not reused the lower cost thermocouple variety is preferred, except that it presents technical problems which tend to increase cost. Unlike the thermistor probe which provides a direct indication of temperature, the thermocouple probe senses the difference in temperature at the hot and cold junctions of the thermocouple whereby some form of compensation is required to convert the measurement of temperature difference to temperature. Past solutions to that problem have added to the cost of the thermocouple probe.
Further, existing instrumentation designed for use with thermistor probes is not compatible with the thermocouple probe. Accordingly, there has been a need, not only for improvement in thermocouple probe systems, but the need extends to finding a solution that would permit use of the improved thermocouple probe with the thermistor probe instrumentation.
Another difficulty arises out of the fact that the temperature-sensing probe may be located at a substantial distance from the signal processing and indicating apparatus with which it is associated. In the hospital and clinical environments in particular, where x-ray machines and other radio frequency generating apparatus creates very strong fields, radio frequency interference with temperature measurement is a difficult and serious problem. The traditional bypassing and radio frequency choking techniques are less than adequate, and the problem is amplified by the compensating techniques heretofore employed in connection with thermocouple sensing.